The objective of this proposal is to develop, validate, and distribute numerical simulation software for comprehensive computer modeling of therapeutic ultrasound. The principal application areas are focused ultrasound for noninvasive treatment of cancer and benign prostatic hypertrophy. Emphasis is on therapy methods that minimize blood perfusion effects via relatively fast, localized heating of tissue. The principal modeling issue is rapid, nonlinear change in tissue and ultrasound propagation in the focus, requiring a combination of non linear thermal and ultrasound modeling for both continuous and transient mechanical waves. No comprehensive modeling capability of this type exists in the medical community today. The analytical bases for this numerical simulation research are time- domain finite element methods. Temporal integration of the finite element equations provides complete linear or nonlinear solutions of the ultrasound and bioheat equations in two-or three-dimensional (2D or 3D) domains that conform to tissue boundaries. The aim is to develop the necessary software and make it accessible to all interested parties, both commercial and academic. The code will run on UNIX workstations and the next generation of personal computers (Pentium and PowerPC). The foundation finite element code, PZFlex is fully operational and currently sold for transducer design.